Custom List With Images in Blackberry

问题

I want to implement something like this in my application:

That is, each image contains one heart icon. I want to handle the click event on heart click and for that I have the following code

list.setEmptyString("No Image Available", DrawStyle.HCENTER);
            list.setRowHeight(Display.getHeight() - 100);
            list.setSize(data.size());
            if (listVManager != null && listVManager.getFieldCount() > 0) {
                listVManager.deleteAll();
            }

            list.setCallback(new ListFieldCallback() {
                public void drawListRow(ListField list, Graphics graphics,
                        int index, int y, int w) {
                    int yPos = y + list.getRowHeight() - 1;
                    graphics.setColor(0x434343);
                    graphics.fillRect(0, y, w, list.getRowHeight());

                    if (logoThumbnailImage != null
                            && logoThumbnailImage.length > index
                            && logoThumbnailImage[index] != null) {
                        EncodedImage img = logoThumbnailImage[index];
                        graphics.drawImage(0, y + 10, Display.getWidth(),
                                Display.getHeight() - 100, img, 0, 0, 0);

                        graphics.drawText("Hello", 10,
                                Display.getHeight() - 150);
                        graphics.drawImage(Display.getWidth() - 70,
                                Display.getHeight() - 150 + 300,
                                heart.getWidth(), heart.getHeight(), heart,
                                0, 0, 0);
                    } else {
                        graphics.drawImage(
                                15,
                                y + 10,
                                Display.getWidth(),
                                Display.getHeight() - 100,
                                sizeImage(iconImage, Display.getWidth(),
                                        Display.getHeight() - 100), 0, 0, 0);

                    }

                    graphics.drawText("Hello", 10,
                            Display.getHeight() - 150);
                    graphics.drawLine(0, yPos, w, yPos);

                }

                public Object get(ListField listField, int index) {
                    return null;
                }

                public int getPreferredWidth(ListField listField) {
                    return Display.getWidth();
                }

                public int indexOfList(ListField listField, String prefix,
                        int start) {
                    return 0;
                }
            });
            listVManager.add(list);
            loadImages = new LoadImages(80, 80);
            loadImages.start();
        }
    });

here load image is thread that load images in background and store them in logoThumbnailImage array and invalidate list from there when the it loads the image.

The Load image thread class:

private class LoadImages extends Thread {

    int widthL;
    int heightL;
    LoadImages(int width, int height) {
        this.widthL = width;
        this.heightL = height;
    }

    public void run() {
        logoThumbnailImage=new EncodedImage[numberOfItem];
        if (object != null) {
            for (int i = 0; i < numberOfItem; i++) {                
                    try {
                        String text=object[i].getJSONArray("UrlArray").getString(0).toString();
                        EncodedImage encodedImg = JPEGEncodedImage.encode(connectServerForImage(text), quality);    //connectserverForImage load Images from server                     
                        logoThumbnailImage[i] = sizeImage(encodedImg, Display.getWidth(), Display.getHeight()-100);
                        list.invalidate();


                } catch (Exception e) 
                {
                        e.printStackTrace();
                    }

            }
        } else {
            UiApplication.getUiApplication().invokeLater(new Runnable() {
                public void run() {
                    Dialog.alert("No Data Found");
                }
            });
        }
    }
}

The application runs smoothly but I got the following output:

I have the following problem 1. The heart and description is displayed on only one list row. Can any one tell me what I am missing? 2. How to perform the click event on heart

回答1:

Having looked at this only briefly, the problem appears to be that you are, in places, ignoring the 'y' position that is passed in to your drawListRow() method:

        public void drawListRow(ListField list, Graphics graphics,
                int index, int y, int w) {

Effectively the 'canvas' that you should be using to paint the current row (the row identified using int index) is bounded by the rectangle (0, y, w, list.getRowHeight()).

In fact, you can actually paint anywhere in the extent that belongs to the ListField, i.e. the area you can paint onto is actually the rectangle (0, 0, list.getWidth(), list.getHeight()). You can do this, but you shouldn't. If you go outside your row's rectangle you will be painting over another row.

In your case, painting outside the selected row is exactly what your code does. You do this:

                graphics.drawText("Hello", 10,
                        Display.getHeight() - 150);

This will actually be positioned on the ListField, 10 pixels in from the left and Display.getHeight() - 150 down from the top. It will be positioned at this point in the ListField, regardless of which row you are painting. So every row will put the Hello text in the same place.

So when coding your drawListRow(), make sure you offset all the positions to stay within the bounds of the row you are supposed to be painting. The origin of the area you are painting is (0, y), so offset all vertical positions using y. Do not use Display.getHeight(), use list.getRowHeight() to get the height you can paint (starting at y), and do not use Display.getWidth(), use the w variable that is passed in to get the width that you can paint. All your graphics actions should occur within these bounds.

来源：https://stackoverflow.com/questions/19273633/custom-list-with-images-in-blackberry